Synergistic cytotoxicity of HIV-PI with bortezomib and carfilzomib. (a) AMO-1 cells were incubated with the respective HIV-PI (0–20 μℳ) in combination with bortezomib 0–5 nM (upper panel), or in combination with carfilzomib (0–5 nM, lower panel), and cell viability was assessed by dimethylthiazol-diphenyltetrazole test. (b) The synergistic cytotoxic effect of nelfinavir, lopinavir, saquinavir, ritonavir with bortezomib (a upper panel), in contrast to the other HIV-PI (Supplementary Figure 3), is statistically confirmed by Isolobograms (symbols below the dashed line statistically indicate synergism).